population and communities Flashcards
(19 cards)
Populations as interacting groups of organisms of the same species living in an area
Students should understand that members of a population normally breed and that reproductive isolation is used to distinguish one population of a species from another.
A population is a group of organisms of the same species who live in the same area at the same time able to interbreed with each other.
Estimation of population size by random sampling
Students should understand reasons for estimating population size, rather than counting every individual, and the need for randomness in sampling procedures.
Sessile moving organisms: quadrat sampling, line or belt transect
- quicker/remove bias
Random quadrat sampling to estimate population size for sessile organisms
Both sessile animals and plants, where the numbers of individuals can be counted, are suitable.
HOW TO ESTIMATE POPULATION SIZE FROM GRID
- Generation of random numbers using a table or a random number generator
- The first random number determines the distance along the tape, the second random number is used to determine a distance out across the habitat at right angles to the tape.
If the presence or absence of more than one species is recorded in every quadrat during sampling of a habitat, it is possible to test for an association.
Calculate the population size by calculating the average number of daisies from all your grids. Multiply this number by 100 so that you know the total number of flowers in the entire field. This is your estimated number
Capture–mark–release–recapture and the Lincoln index to estimate population size for motile organisms
LINCOLN INDEX FORMULA
Students should understand what is indicated by the standard deviation of a mean. Students do not need to memorize the formula used to calculate this. In this example, the standard deviation of the mean number of individuals per quadrat could be determined using a calculator to give a measure of the variation and how evenly the population is spread.
- CAPTURE USING TRAPS OR NETS
- MARK EACH INDIVIDUAL W/ PAINT
- RELEASE ALL MARKED INDIVIDUALS BACK INTO THEIR HABITAT
- RECAPTURE (MARKED+UNMARKED - ANY)
- CALCULATE LINCOLN’S INDEX
LI = M1*R/M2
Carrying capacity and competition for limited resources
A simple definition of carrying capacity is sufficient, with some examples of resources that may limit carrying capacity FOR PLANTS? FOR ANIMALS?
EXAMPLE OF DENSITY DEPENDENT/INDEPENDENT FACTORS
The maximum size of a population that an environment can support is the carrying capacity; Beyond this limit the population cannot increase anymore.
Negative feedback control of population size by density-dependent factors
Numbers of individuals in a population may fluctuate due to density-independent factors, but density dependent factors tend to push the population back towards the carrying capacity. In addition to competition for limited resources, include the increased risk of predation and the transfer of pathogens or pests in dense populations.
3 MAIN TYPES OF DENSITY-DEPENDENT FACTORS
- COMPETITION
- PREDATION
- DISEASE
Population growth curves
Students should study at least one case study in an ecosystem. A lag phase is not expected as a part of sigmoid population growth. Students should understand reasons for exponential growth in the initial phases.
3 STAGES OF POPULATION GROWTH
Exponential, Transition, Plateau
EXPONENTIAL - N&I>E&M; LOTS OF RESOURCES - LIMITING FACTORS ARE NOT RESTRICITNG POPULATION GROWTH
TRASNITION - SOME LIMITNG FACTORS BECOMING SCARCE, INCREASE COMP.
PLATEAU = REACHES CARRYING CAPACITY
REASONS FOR ABSENCE OF DENSITY-DEPENDENT FACTORS; ABSENCE OF PREDATORS, IDEALIZED CONDITIONS
In Switzerland, the bearded vulture became extinct during the 19th century, until repopulation efforts took off and now show a steady increase since 2006. (BREEDING PROGRAMS IN CAPTIVITY)
Modelling of the sigmoid population growth curve
Students should test the growth of a population against the model of exponential growth using a graph with a logarithmic scale for size of population on the vertical axis and a nonlogarithmic scale for time on the horizontal axis.
A community as all of the interacting organisms in an ecosystem
Include reasons for intraspecific competition within a population (NECESSITIES).
Also include a range of real examples of competition and cooperation. (SEE NEXT SLIDE)
A community is a group of populations living together in an area and interacting with each other.
Competition versus cooperation in intraspecific relationships
Communities comprise all the populations in an area including plants, animals, fungi and bacteria.
COMPETITION IN PLANTS: LIGHT, SPACE, SOIL NUTRIENTS, WATER
COMPETITION IN ANIMALS: WATER, NESTING SITES
BENEFITS FROM COOPERATION:
- SOCIAL PREDATION INCREASES SUCCESS
- SCHOOL OF FISH
- PENGUINS HUDDLING, PROVIDING WARMTH
Herbivory, predation, interspecific competition, mutualism, parasitism and pathogenicity as categories of interspecific relationship within communities categories.
Include each type of ecological interaction using at least one example.
HERBIVORY - PRIMARY CONSUMERS FEEDING ON PRODUCERS; APHIDS DRAWING OUT PLANT SAP
PREDATION; ONE CONSUMER SPECIES EATING ANOTHER; LIONS EATING DEER
INTERSPECIFIC COMPETITION; LIONS AND HYENAS FEEDING ON THE SAME PREY
MUTUALISM - 2 SPECIES LIVING IN CLOSE ASSOCIATION THAT BENEFIT FROM EACH OTHER; BIRDS PICKING TEETH OF CROCODILES
PARATISM; ONE SPECIES LIVES IN ANOTHER AND OBTAINS FOOD FROM THEM, HARMING HOST; TICKS
PATHOGENICITY - One species (the pathogen) living inside another species (the host) and causing a disease in the host; POTATO BLIGHT FUNGUS
Mutualism as an interspecific relationship that benefits both species
Include these examples: root nodules in Fabaceae (legume family), mycorrhizae in Orchidaceae (orchid family) and zooxanthellae in hard corals. In each case include the benefits to both organisms.
- Root nodules in Fabaceae:
* Rhizobium bacteria live in root nodules of plants in the legume family
* Bacteria perform nitrogen fixation; conversion inert nitrogen (N2) into ammonia (NH3) that can be used by plants as fertilizer
* In exchange, plants provide carbohydrates and a favorable environment for bacteria - Mycorrhizae in Orchidaceae:
* Mycorrhizae are symbiotic relationships between fungi and plants
* Orchid seeds do not have sufficient nutritional reserves to germinate on their own
* Fungi obtain nutrients from the environment and pass it on to the orchid seed
* When the orchid plant dies, the fungi benefit by decomposing it - Zooxanthellae in hard corals:
* Zooxanthellae are photosynthetic algae that live in the tentacles of coral polyps
* Zooxanthellae provide carbon-based energy for coral polyps
* Coral polyps (which make up coral reefs), in exchange, provide algae with the minerals and CO2 they need to photosynthesize, in addition to providing a safe environment for their growth
Resource competition between endemic and invasive species
Choose one local example to illustrate competitive advantage over endemic species in resource acquisition as the basis for an introduced species becoming invasive. (JAPANESE KNOTWEED)
Invasive species compete for resources with endemic species and often cause them to occupy smaller niches, decline in population size or become entirely extinct.
Invasive plant growing up to 3m high and with a very extensive root network. Grows preferably close to riverbeds, where it pushes back endemic plants which are better suited to the terrain. It grows in between bricks and walls causing breakage and destruction. Along riverbeds it contributes to destabilization of soil.
Tests for interspecific competition
Interspecific competition is indicated but not proven if one species is more successful in the absence of another.
Students should appreciate the range of possible approaches to research: laboratory experiments, field observations by random sampling and field manipulation by removal of one species.
CHECK ASSOCIATION USING CHI SQUARED TEST
There are two possibly hypothesis:
H0: Two species are distributed independently
H1: Two species are associated.
Use of the chi-squared test for association between two species
Students should be able to apply chi-squared tests on the presence/absence of two species in several sampling sites, exploring the differences or similarities in distribution. This may provide evidence for interspecific competition.
SEE SLIDE 59!!!!
EV = ROW TOTAL*COLUMN TOTAL/GRAND TOTAL
SUM OF (O-E)^2/E
This calculated value needs to be compared to a critical value in order to obtain knowledge about the statistical significance of this result.
NB: For statistical tests on association the degrees of freedom are always 1.
P > 0.05; ACCEPT ALT. HYPOTHESIS
P < 0.05; ACCEPT NULL HYPOTHESIS
Predator–prey relationships as an example of density-dependent control of animal populations
Include a real case study.
RED FOX & MOUNTAIN HARE IN SWEDEN; FOX POPULATIONS DECLINED SIGNIFICANTLY AFTER A DISEASE SPREAD AMONG THEM, INCREASING MOUNTAIN HARE POPS. (LATE 1980S)
Top-down and bottom-up control of populations in communities
Students should understand that both of these types of control are possible, but one or the other is likely to be dominant in a community.
Top-down control acts from a higher trophic level to a lower one. An increase in predator number will decrease the population size of the prey.
Bottom-up control acts from a lower trophic level to a higher one. A population of producers may be limited by the number of nutrients in soil or water; E.G., The amount of seaweed available on the floor of the sea will determine the number of sea turtles feeding on them, and therefore have an impact on the consumers higher up the food chain.
Allelopathy and secretion of antibiotics (WAYS TO DETER COMPETITORS FROM THEIR ECOLOGICAL NICHE)
These two processes are similar in that a chemical substance is released into the environment to deter potential competitors. Include one specific example of each—where possible, choose a local example.
Allelopathy is the release of chemicals as secondary metabolites or toxins by plants, which are given off into the soil to prevent nearby competitive plants to grow in the same area.
Many fungi produce antibiotic substances which prevent the growth of other species (e.g bacteria) by interfering with cell wall components of them, which eventually cause them to burst and die.
